United States 'stealth' fighters sent to South Korea for a training exercise are to stay on once the exercises end, a US military statement said on Tuesday.
The decision will anger North Korea, which has warned that the US is building up its troops in the region in preparation for an attack.
The US sent six F-117A radar-evading airplanes to South Korea in March as part of annual military exercises.
"Extending their training time in the Korean Theatre of
Operations affords an excellent opportunity to further
enhance interoperability while also enhancing deterrence," the US statement said.
It came on the same day that North Korea was reported to have fired a short-range anti-ship missile off its west coast.
Initially the Japanese Defence Agency said the missile was launched at about 1015 local time (0115 GMT) from North Korea's north-west coast, and that it constituted no threat to Japan.
However the report, which was dismissed by South Korean officials, was later retracted by Japan.
The confusion deepened later on Tuesday when a Pentagon official said the Pentagon believed the North Koreans had carried out a new missile test.
The Pentagon was not alarmed by the missile test, the official said, but he described it as not particularly helpful given the current level of tensions.
North Korea has tested two missiles in recent months, raising fears it was about to end its moratorium on longer range, ballistic missile tests.
There had been speculation that the communist state was preparing to test-fire a medium-range Rodong missile last Friday - to coincide with Japan's launch of two spy satellites.
The satellites are designed to give Japan its own independent means of gathering intelligence from the reclusive state.
North Korea denounced the move, calling it a hostile act that could spark a new arms race.
North Korea has been engaged in a stand-off over its nuclear ambitions since it reactivated its nuclear plant at Yongbyon and pulled out of the global nuclear arms control treaty.
Little headway has been made in efforts to get Pyongyang to take part in talks to resolve the six-month-old crisis.